Why CFLi light doesn't look quite right

I just read an online discussion about energy saving Compact Fluorescent lights. Some people complained they didn't like the quality of light, and they were criticised by others.

CFLi lamps don't make the same quality of light as incandescents. They can't. Fluorescent lamps synthesize white light by the powder on the inside of the tube. Each type of powder makes one color of light. Nearly all CFLi lamps have a mix of three phosphors chosen to create white light (in fact, the phosphors on pre-flatscreen TVs worked this way). But there are missing colors in the spectrum. If you put CFLi light through a glass prism, you won't get a full rainbow because not all colors are there. That's why CFLi light means that things don't look quite right; you can't see a color if that color light is not in the room (think of trying to recognize a green car under those old orange car-park lights). White LEDs do the same thing, so this problem is not going away. High quality office fluorescents use more than three phosphors to get better color rendering, but then you lose energy efficiency.

Old-fashioned light bulbs make light by heating something until it glows brightly. This is the same way the sun works and guarantees a smooth and complete color spectrum, so incandescent lamps make much more natural light. They are bad for energy efficiency since this way of working makes more heat than light, but they do make nice light.

Technically, the way to measure the completeness of color in a light bulb is to look at the Color Rendering Index. Sunlight has an index of 100. You'll easily notice inferior light when the number gets down below 90 (in my opinion). CFLi lamps are low pressure mercury vapor lamps, which means they make ultra-violet light. The phosphor powers convert this to visible light, mostly. You still get more ultraviolet coming out of a CFLi than from an incandsescent, which is why we are unlikely to see fluorescent lights in art galleries (UV destroys things). Another difficulty with CFLi lamps is the warm-up time. They take 60 to 90 seconds to reach brightness because the mercury in the lamp needs to fully evaporate into the vapor. If the lamp gets too hot (inside a light fixture, or covered with an outer shell) then the efficiency of the lamp falls away and the light gets dimmer. Special mercury compounds address this problem, but these require sophisticated manufacturing techniques largely out of the reach of cheap manufacturers.

Why do compact fluorescents die? For pretty much the same reason old fashioned light bulbs end their life: a small piece of metal slowly evaporates away as the light bulb is turned on. That's why you see black or dark staining on old compact fluorescents. In an old-fashioned light bulb, the filiament eventually gets too thin and breaks. In a CFLi, the small piece of wire than launches the current into the glass tube breaks or just slowly disappears. The most stressful time for a compact fluorsecent is when it's turned on: a surge of current flows through the cold lamp. This is so damaging to the lamp that the life of a compact fluorescent is specified in hours of burning AND "switching cycles" (number of times turned on). Most domestic fluorescents have low switching life, and won't reach advertised life times in hours if you switch the light on and off a lot. The manufacturers often don't tell you, but the "10,000 hour" lifetime typically assume you switch the light on only once a day. Better electronics can dramatically reduce the damage of switching the light on, so professional compact fluorescents have much, much better lifetimes. At least in Europe, some supermarket light bulbs by the big brands also have this protection, but to be frank, if your lamp is made in China, it's unlikely to. Switching "shock abosorption" costs more, but not much more. A reason not to buy from the supermarket.

Some more things to know: The electronics in a home compact fluorsecent are part of the lamp and thrown out at end of life. So there's not much point putting expensive electronics into the lamp, and unfortunately it requires expensive electronics to properly dim this type of light source. Professional fluorescents use expensive permanent electronics and replacement light bulbs, which is why you get excellent dimming from modern office fluorescents. The cheap electronics in home domestic light bulbs disturb the power supply, so you shouldn't use lots of them in one place.